# What should length of copper coil be to heat fluid from Temp A to Temp B?

I'm building a milk pasteuriser.

The milk in the cooling tank has a starting temperature of 4°C. It should then be heated to 72°C for 30 sec, then cooled back down again to 4°C as quickly as possible (if I understand the process correctly).

I've got 2 bulk tanks, one with a heating fluid of 90°C and another with cooling fluid of 4°C.

My question is this: What should the length of each of the copper induction coils be to heat/cool the fluid to the appropriate temperature for the required length of time. (I'm looking for a formula if such exists)

**Side note: I'm not an engineer. I'm a home hobbyist with background in maths/programming.

• The solution is going to require the flow rate, the tube diameter, wall thickness and, possibly, some measure of turbulence in the pipe. "As quickly as possible" isn't really a good specification. Very quickly is possible but how much are you prepared to spend? If I was attempting this I would be inclined to pump the milk through a pasteuriser coil in the hot tank, through a cooling coil and back to storage. Your question reads as though you are going to heat and cool the whole storage tank-load of milk. – Transistor Feb 16 at 11:00
• There may be some opportunity for improved energy efficiency by using a heat exchanger to transfer the recovered heat into the incoming cold milk. – Transistor Feb 16 at 11:00
• @Transistor, assuming I have the flow rate, tube diameter, etc., what would be the formula to use? – ljc Feb 20 at 14:33